During the course of medical treatment, it is often necessary to deliver pharmaceutical compositions (e.g., tissue bulking materials, bone fillers, contrast agents, drugs, growth factors, etc.) to a target tissue site by injection. In general, a hollow needle or cannula with a syringe attached to it is inserted at or near the target tissue and the pharmaceutical composition delivered. At the time of injection, pressure is exerted in the syringe to expel the pharmaceutical composition at or near the target tissue site.
Sometimes, particularly with viscous compositions, such as for example, in situ setting materials, gels, bone cements, and other pharmaceutical compositions, the practitioner will exert excessive pressure to expel the pharmaceutical composition from the needle or cannula. This excessive pressure may rupture the target tissue causing damage to the tissue and/or leakage of beneficial physiological fluid. For example, when treating a spinal disc annular tear or herniation, the practitioner will often administer an in situ setting material at or near the site of the disc injury. If the in situ setting material is administered under excessive pressure, this can cause further trauma to the disc area by causing the nucleus pulposus (the jelly-like substance in the middle of the spinal disc) to leak out of the annulus fibrosus (the fibrous ring of the intervertebral disc) leading to further annulus tearing or herniation and/or painful debilitating effects on the patient by compressing the spinal canal and the spinal nerve root.
The pain from the annular tear or herniated disc may be further exacerbated as the nucleus pulposus contains significant amounts of substances capable of exciting, or increasing the excitability of, sensory nerves such as prostaglandin E, histamine-like substances, lactic acid and polypeptide amines. These substances may also escape increasing the lower back pain or cause radiating leg pain. In addition, the increased pressure from the injection may increase the size of any annular tear present in the disc, which may cause fibrous tissue to grow into the tear, which also increases pain and/or inflammation.
Excessively high pressure injections can damage other tissues such as blood vessels causing blood and/or the pharmaceutical composition to leak into surrounding tissues that are not intended to be the target of the therapy. This may also cause pain, inflammation, edema, scars and often times, necrosis of the surrounding tissue or even an embolism.
High pressure injections may also lead to the practitioner giving too much of the pharmaceutical composition too soon which can be detrimental to the patient due to adverse effects of the sudden dose of the pharmaceutical composition. For example, sudden administration of pharmaceutical compositions can cause fluid overload at or near the target tissue site, which may cause edema, hypertension, electrolyte imbalance, or in severe case heart failure. This is particularly so when administering very potent pharmaceutical compositions that have a low therapeutic index, even small quantities administered too soon to the patient can be detrimental.
Sometimes, if too much pressure is used to expel the pharmaceutical composition from the syringe, the composition may migrate away from the target tissue site leading to reduced efficacy of the composition or even damage to surrounding tissue. For example, when using bone cements or fillers that are administered in a flowable state and later harden after administering them at a target tissue site, if the bone cement or filler is expelled from the needle or cannula at an excessive pressure, it may migrate to surrounding tissue and harden in the wrong area (e.g., such as a healthy joint or vertebrae) which may severely inhibit movement of the joint. In more severe cases, the bone cements or fillers may migrate to a blood vessel and cause an ischemic event (e.g., embolism, necrosis, edema, infarction, etc.), which could be detrimental to the patient.
In light of this background, there exist needs for improved devices and methods for injecting pharmaceutical compositions at or near a target tissue site.